package class03;

/**
 * @author zhangchaoliang
 * create 2022
 */
public class ReversePair2 {

    public static int reverPairNumber(int[] arr){
        if (arr==null||arr.length<2)
            return 0;
        return process(arr,0,arr.length-1);
    }

    public static int process(int[] arr,int L,int R){
        if (L==R)
            return 0;
        int mid = L+((R-L)>>1);
        return process(arr,L,mid)
                +process(arr,mid+1,R)
                +merge(arr,L,mid,R);
    }

    public static int merge(int[] arr,int L,int M,int R){
        int[] help = new int[R-L+1];
        int i = help.length-1;
        int p1=M;
        int p2=R;
        int res = 0;
        while (p1>=L&&p2>M){
            res+=arr[p1]>arr[p2]?(p2-M):0;
            help[i--]=arr[p1]>arr[p2]?arr[p1--]:arr[p2--];
        }
        while (p1>=L)
            help[i--]=arr[p1--];
        while (p2>M)
            help[i--]=arr[p2--];
        for (i=0;i<help.length;i++)
            arr[L+i]=help[i];
        return res;
    }

    public static int comparator(int[] arr){
        if (arr==null||arr.length<2)
            return 0;
        int ans = 0;
        for (int i=0;i<arr.length;i++){
            for (int j=i+1;j<arr.length;j++){
                if (arr[i]>arr[j])
                    ans++;
            }
        }
        return ans;
    }

    public static int[] generateRandomArray(int maxSize,int maxValue){
        int[] arr = new int[(int)((maxSize+1)*Math.random())];
        for (int i=0;i<arr.length;i++)
            arr[i]=(int)((maxValue+1)*Math.random())-(int)((maxValue+1)*Math.random());
        return arr;
    }

    public static int[] copyArray(int[] arr){
        if (arr==null)
            return null;
        int[] res = new int[arr.length];
        for (int i=0;i<arr.length;i++)
            res[i]=arr[i];
        return res;
    }

    public static boolean isEqual(int[] arr1,int[] arr2){
        if ((arr1!=null&&arr2==null)||(arr1==null&&arr2!=null))
            return false;
        if (arr1==null&&arr2==null)
            return true;
        if (arr1.length!=arr2.length)
            return false;
        for (int i=0;i<arr1.length;i++){
            if (arr1[i]!=arr2[i])
                return false;
        }
        return true;
    }

    public static void printArray(int[] arr){
        if (arr==null)
            return;
        for (int i =0;i<arr.length;i++)
            System.out.print(arr[i]+" ");
        System.out.println();
    }

    public static void main(String[] args) {
        int testTime = 50000;
        int maxSize = 100;
        int maxValue = 100;
        System.out.println("test begin!");
        for (int i=0;i<testTime;i++){
            int[] arr1 = generateRandomArray(maxSize,maxValue);
            int[] arr2 = copyArray(arr1);
            if (reverPairNumber(arr1)!=comparator(arr2)){
                System.out.println("Oops!");
                printArray(arr1);
                printArray(arr2);
                break;
            }
        }
        System.out.println("test end!");
    }
}
